It's important to socialize your dogs SAFELY with all types of dogs. When I say all types - each like us have different ways of interacting with each other. It is important to expose them so they get conditioned.
Today Boo who is a big play monkey found Timmy overwhelming at first. Why? Timmy has this fun, bowl you over, I am here spirit and Boo wasn't sure how to handle that. As time went on and it was a short time, they started playing and Boo understood the communications and the intentions. Both are puppies about the same age and are learning.
If you do not expose your dogs (this is why we have so many play dates etc) it is more difficult as an adult and a slower process to gain these communication understanding skills. But don't give up. Never say never. They can and do gain those skills as adults. They are just more set in their ways and not as trusting and receptive at times so the process is longer.
By socializing you help them gain their social skills, become more confident and understand the variety of ways each dog communicates and be able to pick up on the similarities and gain that understanding quicker each time they get exposed.
The critical stage is that first year but they need to socialize SAFELY throughout their lives. When doing so, you will appreciate the result!